There are applications in which it is desirable to direct a light beam to any point in a three-dimensional space. Often, the light beam must be switched between two points with high speed. To satisfy this need, two-dimensional beam-steering systems based on rotating micromechanical mirrors have been developed.
Micro-Electro-Mechanical Systems (MEMS) technology has been widely applied to optical beam-steering applications. MEMS devices are capable of switching speeds on the order of tens of kHz and are therefore well-suited to optical applications that require switching times of a few hundred microseconds.
But there are applications, such as atomic-based quantum computing, that require switching speeds on the order of 1 microsecond. In a quantum processor, a light beam is used to interrogate particles, referred to as qubits, which are located within a two-dimensional lattice. Qubits are typically electrons, photons, or ions whose charge or polarization can be changed by shining light of a particular wavelength on them. These qubits are typically separated from one another within the lattice by only a few microns.
High-speed switching is particularly important in quantum processing because qubits must typically be addressed (illuminated) at frequencies greater than 1 MHz to keep them from randomly changing state. Because MEMS devices have been inadequate for this application, switching devices based on acousto-optical or electro-optical deflectors have been used. Although they possess the requisite speed, these devices exhibit other drawbacks.
In particular, acousto-optical or electro-optical deflectors are difficult to wavelength tune and are typically suitable for only a single wavelength. Also, acousto-optical deflectors induce small frequency shifts in the laser that must be managed. These issues are problematic because different qubits in the processing lattice will sometimes require different, specific wavelengths of light to effect a phase change. For example, a trapped ion might require ultraviolet light (of a specific wavelength), while a trapped neutral atom might require infrared light. In fact, a single qubit might require two different wavelengths of light at the same time to cause a phase change.
Additional drawback are that acousto-optical deflectors are power intensive and electro-optic deflectors require large operating voltages while providing only limited angular range.
A beam-steering system that is readily tunable and that is capable of high speed switching with position resolution of a few microns would therefore represent a significant advance in the state of the art.